I know this is a necro-thread and most of the info in here is very out-of-date, but I figured I would share this "solution" here. One of the serious problems with the addons manager is that the code that ships with the default theme is filled with all kinds of weird styling junk. You can force Firefox/SeaMonkey to rip out this junk and use OS-native styles by using -moz-appearance. NOTE: you cannot "theme" the elements after you've applied an OS appearance. This is essentially then just a quick-and-dirty way of killing the default styling. You can use it in conjunction with the binding I posted here to get something that looks close to the Firefox 3.x addons manager without much work: